To unify terminology, recognize their similarity to IDH-mutant WHO Grade 2 and 3 astrocytomas, and add grading within glioma types, the 2021 WHO Classification eliminated the old “glioblastoma IDH-mutant WHO Grade 4” and replaced it with “astrocytoma IDH-mutant WHO Grade 4.”2 The gene discussed is IDH1; the disease is central nervous system cancer.